<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      let arr = [1, 2, 3, 4, 5];
      // 查找顺序是从左侧，还可以继续指定查找的位置
      console.log(arr.indexOf(2));

      // 查找顺序从右侧
      console.log(arr.lastIndexOf(2));

      if (arr.includes(2)) {
        console.log("找到了2");
      }
    </script>
  </body>
</html>
